Our overall objective is to gain an understanding of the mechanism(s) by which the pigment epithelium (PE) supports the normal functioning of the neural retina. This ultimate goal can be reformulated into the following immediate goals: to obtain a greater understanding of PE ion and metabolite transport; to assess the contribution of potassium to electroretinogram slow waves and to long-term changes in the standing potential; to determine if the PE buffers extracellular potassium; to assess PE involvement in spreading depression of the inner retina; to determine if the PE interacts with the cones in the same way that it interacts with the rods; to obtain an understanding of the passive and active ionic mechanisms of mammalian PE; to describe hormonal control of disc shedding and phagocytosis in Xenopus. It is proposed to study these PE mechanisms and PE retina interactions with a combined electrophysiological, epithelial-transport and anatomical approach.